How to get better TAD? Relationship between anteversion angle of nail and position of femoral neck guide pin during nailing of intertrochanteric fractures

Abstract Background To demonstrate the correlation between guide pin-shaft angle (PSA) at the anteroposterior film and anteversion angle of guide pin at the lateral film and investigate whether excellent tip–apex distance (TAD) can be obtained by changing the entry point via axial rotation of the main intramedullary nail. Methods Fifty patients with intertrochanteric femoral fractures (IFFs) undergoing internal fixation with intramedullary nails under 2D fluoroscopy were retrospectively enrolled. Both of the PSA at the anteroposterior film and anteversion angle at the lateral film before and after adjustment of the guide pin were collected. Pearson correlation analysis was performed to investigate their correlation. Intraoperative and postoperative outcomes were recorded. Furthermore, the software of Mimics 10.0 and Pro/E were used to establish the 3D models of the proximal femur and main intramedullary nail/guide pin, respectively. Surgery was simulated on the Pro/E software platform and solid geometry analysis was conducted to calculate the correlation between the PSA and the anteversion angle. Results Pearson correlation analysis indicated there was a positive correlation between PSA and anteversion angle, with the correlation coefficient of 0.902 (p < 0.01). By altering the PSA and anteversion angle, TAD was adjusted to be less than 25 mm in all patients. The mean operative time, fluoroscopy time and length of hospital stay were 65.82 ± 11.16 min, 2.03 ± 0.79 min and 6.66 ± 2.49 d. Thirty-one patients received blood transfusions (3.55 ± 1.95 U). Fracture reduction was considered to be good or acceptable in all patients. Complications occurred only in 6 patients (12.00%). At a 3-month follow-up, the mean Timed Up and Go was 31.54 ± 20.95 s and Harris Hip Score was 72.88 ± 8.79. The 3D surgery model also showed when the main intramedullary nail was externally rotated or internally rotated of 20° at the standard location, the PSA of guide pin at the anteroposterior position and anteversion angle of the guide pin at the lateral position were simultaneously increased or decreased. Conclusion Our findings suggest altering the PSA and anteversion angle may be beneficial for obtaining excellent TAD and achieving superior outcomes.